Thursday, February 14, 2019

Season 14 superfinal, games 41-50

After 50 games Leela leades 7-6 with 37 draws.
Finally a decisive game after 19 straight draws. For the first time in the match Leela is in the lead.

Leela's eval started above 1 in game 41, it increased rapidly and was over 2 on move 12. Stockfish was up a pawn, the engines castled in opposite directions, the white king was exposed on the queen side but relatively safe. It was the black king that seemed threatened by Leela's pawns and pieces. After exchanging queens Leela's eval jumped even higher and Leela regained the pawn. There was no immediate threat but Leela saw a long term advantage, perhaps its king side pawn majority.

Stockfish exchanged down to a knight ending on move 35. Leela's eval remained over 2 as the engines shuffled. After a while Stockfish's eval came down to 0 and Leela's eval started to decrease slowly. The game ended in a tablebase draw on move 175.
In the reverse game both engines didn't castle and both kings moved forward. Leela gave a bishop for 3 pawns, clearing the queen side and exposing the white king. Stockfish protected its king with its pieces. Evals came down and the game reached a RNN vs RB position on move 39. Leela pushed a pawn to the 7th rank before the game was adjudicated by the draw rule.

Games 43-44 started with a 21-ply book sequence of the Sicilian Velimirovic attack opening. The games diverged only on move 21 with castling in opposite directions and evals around 0.5. In game 43 Stockfish's eval was 0. Leela attacked the black king, Stockfish countered on the queen side and captured two pawns. The game reached a QRB vs QRN position with both kings exposed to checks. On move 63 the engines reduced to a queens ending, a draw was agreed 30 moves later. In game 44 the engines reduced to a RB vs RB ending on move 27. Evals came down quickly, after exchanging the rooks the game was adjudicated in an opposite color bishops position.

Evals were low at the start of game 45. Leela pushed pawns on the king side and Stockfish pushed pawns on the queen side, with almost no exchanges until move 23. Then a long series of exchanges left a RBB vs RBN position on move 33, Stockfish was a pawn up with an advanced passer and a weak knight, its eval was 0. Leela's eval slowly came down as the engines shuffled. The game continued with a few exchanges until adjudicated on move 128. In game 46 the engines kept the pieces on the board and exchanged only a few pawns, the first piece exchange was on move 38. The engines shuffled and exchanged pieces for a very long time. The game reached a N vs B ending and the engines agreed to a draw on move 173.

There were many early exchanges in game 47, the game reached a RRB vs RRB position on move 26, Stockfish's eval was 0. After exchanging a pair of rooks Leela gave the bishop for 4 pawns, there were only white pawns left, 3 on the queen side and 1 on the king side. Leela thought it was better with an eval over 2, but it couldn't break Stockfish's defense. It tried to push the pawns forward, Stockfish captured 2 pawns and forced a draw. In game 48 Stockfish pushed pawns on the king side and left its king exposed. Leela castled short with a white pawn on h6, evals stayed below 1. Stockfish opened the king side on move 33 and evals jumped, the game reached a RNN vs RBN position withevals close to 1.5. However Stockfish could only capture a pawn, it had a doubled passer that Leela blocked and evals gradually came down. The engines shuffled in a BB vs BN ending, the game was adjudicated on move 129.

Leela started game 49 with an eval over 1. Using a knight maneuver it managed to get a protected passer to e6 and its eval jumped over 2.

Stockfish focused on blocking the passer, Leela exchanged pieces gradually as evals crept slowly upwards. Stockfish started to feel the danger, its defenders were cramped and its king also had to be protected. Leela's eval jumped over 4, Stockfish finally got rid of the white passer and after a series of exchanges only RB vs RN were left.

Material was equal but the black pawn structure was a mess. Leela pushed its king side pawns and created connected passers. The game was adjudicated with Leela two pawns up in a winning position. First decisive game after 19 draws.

In the reverse game Stockfish's eval was around 1 after the start. The engines played a long PV agreement line that resulted in a RRN vs RRN position on move 22. Stockfish went a pawn up but the engines kept exchanging pawns and pieces until the game reached a tablebase draw on move 42. Leela wins this game pair and is leading the match.